Since the history of lighting began over 100 years ago with incandescent lamps converting electricity into light, filaments and discharge luminescence light sources have been widely used. However, such filaments and discharge luminescence light sources are problematic because of high power consumption and poor durability. Further, they have disadvantageously low energy efficiency because most of the supplied power is dissipated in the form of heat, while converting only about 5-28% of energy into light. Also, LEDs have been more important as a substitute for conventional light sources due to recent environmental concerns.
LEDs typically do not contain any mercury component and are thus eco-friendly. They have a long lifespan of at least fifty thousand hours and a high energy efficiency of about 90%, as compared to incandescent lamps that have low energy efficiency. Therefore, the scope of application of LEDs has been gradually broadened.
Interior lighting techniques employing an LED light source enable light emitted from the LED to pass through a transparent cover (e.g., a transparent acryl cover) to provide direct lighting, or to pass through a diffusion cover (e.g., a diffusion acryl cover) to provide indirect lighting. Currently, it is necessary to use separate lighting systems adapted for direct lighting and indirect lighting, respectively.
Further, in order to provide two or more correlated color temperatures (CCTs), it is currently necessary to employ LEDs having respective CCTs, resulting in an undesirable increase in the manufacturing costs of the lighting system.
Thus, there has been a demand for the development of novel LED lighting systems capable of addressing the above problems.
Meanwhile, as thin-film materials having various functions have been developed and researches on liquid crystal materials have been made, films capable of adjusting light transmittance or haze have recently been developed. Such a haze-changeable film or a transmittance-changeable film is manufactured by employing functional materials such as liquid crystals and suspended particles.
In a haze- or transmittance-changeable film using liquid crystals or suspended particles, the liquid crystals or suspended particles are interposed between two transparent conductive films. When an electric field is not applied, the liquid crystal molecules or suspended particles are randomly oriented. The haze of the film is maximized since light is scattered, thereby rendering the film opaque. On the other hand, when an electric field is applied, the liquid crystal molecules or suspended particles are well oriented. In such case, light passes through the film, thereby rendering the film transparent. Therefore, the average transmittance of visible light may be adjusted by controlling the intensity of an electric field.
For example, Korean Patent No. 318868 discloses liquid crystals including ferroelectric/antiferroelectric liquid crystal materials and a polymer comprised of urethane acrylate and (meth)acrylate, and a haze-changeable film using same.
Such a haze-changeable film is spotlighted for an increase in its demand, and there have been attempts to apply it to various fields.